This invention relates to block copolymers comprising one or more blocks of a poly(heteroaromatic) polymer and two or more blocks of a non-conjugated polymer and to methods for their preparation. The poly(heteroaromatic) blocks can be either in the neutral state or in the doped state. When the blocks of the poly(heteroaromatic) polymer are in the doped state the resulting block copolymer is electrically conducting and soluble or dispersible in water, an organic solvent, or a mixture thereof. In this invention the poly(heteroaromatic) blocks are referred to as “A”, while the non-conjugated blocks are referred to as “B”. This invention relates to tri-block copolymers of the structure BAB, multi-block copolymers of a minimum of four blocks and structure of ABAB (or longer), and end-capped multi-block copolymers of structure BABAB (or longer).
Intrinsically conducting polymers (ICP) are polymers whose electrical and optical properties can be reversibly controlled by changing their oxidation state. Most ICPs are conjugated polymers with extended π conjugation along the molecular backbone. By chemical or electrochemical oxidation or reduction of the polymer backbone (doping) it is possible to systematically vary the electrical conductivity of these materials from the insulating state to the conducting state. In the doped (conducting) state, ICPs consist of rather rigid planar polyionic chains in which the charges are delocalized over a segment of the backbone. The chains are polycationic when they are doped through oxidation (p-doping) and polyanionic when they are doped through reduction (n-doping). Counter-ions (anions for p-doped polymers and cations for n-doped polymers) are present within the polymeric matrix to compensate for the charges on the polymer.
Representative ICPs include polyacetylene, polyaniline, polypyrrole, polythiophene, poly(phenylenesulfide), poly(paraphenylene), poly(phenylenevinylene), and many others (P. Chandrasekhar, Conducting Polymers, Fundamental and Applications, Kluwer Academic Publishers, Boston, 1999). Because of their extended π conjugation, conducting polymer chains behave like rigid rods, have poor flexibility, and hence do not flow or melt. Therefore, traditional melt processing cannot be employed to process these materials. Moreover, because of the strong ionic interactions among polymer chains and counterions, most conducting polymers do not dissolve in either aqueous or organic solvents and, as a result, cannot be processed from solution (Wessling B.; “Dispersion as the Key to Processing Conducting Polymers”, in Handbook of Conducting Polymers, 2nd Ed.”, Ed. T. A. Skotheim, R. L. Elsenbauer, J. R. Reynolds, (1998), Marcel Dekker, New York, p-471-473). The poor processability of conducting polymers is a major impediment to their commercial use.
A few exotic solvents have been discovered for some conducting polymers. For example, polyaniline doped with organic sulfonic acids is soluble in m-cresol or
hexafluoroisopropanol solutions. These solvents are toxic or expensive, and difficult to handle in a large scale process (Rasmussen P., Hopkins A., Basheer R., Macromolecules, 29, (1996) 7838-7846). Other conducting polymers have been stabilized as diluted dispersions in water. For example, a 1.3% aqueous dispersion of poly(3,4-ethylenedioxythiophene), PEDOT (Formula 1) doped with polystyrene sulfonic acid is commercially available from Bayer AG and is sold under the trade name of Baytron (Trademark, Bayer A G) P (L. Groenendaal, F Jonas, D. Freitag, H. Pielartzik, J. Reynolds, Advanced Materials, 12, (2000) 481494). Conducting polymers containing long solubilizing side-chains such as poly(3-hexylthiophene) are soluble in many common organic solvents such as chloroform, but the side chains often disrupt the conjugation and conductivity is greatly reduced, except for the case of regioregular poly(3-hexylthiophene) which has highly ordered crystal packing. Also the thermal and oxygen stability of these ICPs substituted with solubilizing chains is often much worse than the parent polymer. Finally, substituted monomers are much more expensive than unsubstituted monomers.
Francois and Olinga reported the preparation of polystyrene-polythiophene (PSt-PTh) copolymers by polymerization of thiophene or 2-bromothiophene and polystyrene chains terminated with thiophene or 2-bromothiophene groups. Soluble and insoluble fractions were recovered after synthesis. The soluble fraction was doped in solution after purification by iron chloride. The doping of the copolymer was observed by measuring the optical density of the doping band as a function of the iron chloride loading, but no conductivity data were presented for the copolymer. The copolymer was used to cast films from solution, and these films were then pyrolyzed at 380° C. to de-polymerize the polystyrene. The conductivity of the pyrolyzed films containing only the PTh, was reported to be up to 60S/cm (B. Francois, T. Olinga, Synthetic Metals, 55-57 (1993) 3489-3494). Frangois and others also described the synthesis of poly(paraphenylene) (PPP), polythiophene (PTh), and poly(3-hexylthiophene) block copolymers with polystyrene (PSt) or polymethylmethacrylate (PMMA) by a similar method. Although they stated that “FeCl3 doped PSt-PPP copolymers” formed “exceptionally regular porous and conducting membranes”, no conductivity data were reported (B. Francois, G. Widawski, M. Rawiso, B Cesar, Synthetic Metals, 69 (1995) 463466; R. Lazzaroni, Ph. Leclere, V. Parente, A. Couturiaux, J. Bredas, B. Francois, Synthetic Metals, 102 (1999) 1279-1282).
Xue and others reported the electrochemical copolymerization in nitromethane of pyrrole and styrene at different feed ratios. The formation of block copolymers was reported. The products deposited as insoluble films at the electrode during synthesis, and were insoluble in both nitromethane and dichloromethane. Conductivities ranging from 0.2 to 0.007 S/cm were reported (G. Xue, S. Jin, X. Liu, W. Zhang Y. Lu, Macromolecules, 33, (2000) 4805-4808).
Hadziioannou and others reported the synthesis of block copolymers by regularly alternating a block of oligothiophene with a block of oligosilanylene. The oligothiophene blocks with a specific and definite number of monomer units (thiophene) were first prepared using organometallic chemistry (Ni-catalyzed Grignard coupling of mono- or di-bromothiophenes or by oxidative coupling of lithiated thiophenes). The oligothiophene blocks were then joined with thiophene terminated silanylene blocks (G. Hadziioannou, P. Hutten, R. Gill, J. Herrema; J. Phys. Chem., 99, (1995) 3218-3224). Hadziioannou and others describe using the silanylene group to limit the conjugation length of conducting polymer segments as a method of controlling the luminescence wavelength. The silanylene blocks contain only one or two silicon atoms and are described solely to break the conjugation of oligothiophenes.
Leung and Ho Tan reported the synthesis of polystyrene-polyacetylene di-block copolymers obtained by thermal elimination of polystyrene-poly(phenyl vinyl sulfoxide) di-block copolymers. Conductivity of the copolymers versus compositions is reported (L. Leung, K Ho Tan, Macromolecules, 26, (1993) pp. 4426). Polyacetylene is a conducting polymer but not a poly(heteroaromatic) polymer.
Goodson and others reported the synthesis of rigid/flexible alternating block copolymers of PPP-PEG (poly(paraphenylene)-poly(ethylene glycol)). The copolymers were characterized by thermogravimetric analysis, differential scanning calorimetry and fluorescence spectroscopy, but no conductivity data were reported (Z. Wagner, T Roenigk, F. Goodson, Macromolecules, 34, (2001) 5740-5743). Goodson et al. report the formation of soluble block copolymers when the PPP segment is less than 6 repeat units long. Although PPP forms a conducting polymer, oligomers of 5 repeat units or shorter are non-conducting. Although Goodson and others report the formation of block copolymers of PPP that exhibit fluorescence behavior, they do not report the formation of conducting materials, or materials that can be rendered conducting by doping.
Cao and others reported the synthesis of ABA block copolymers of polyaniline (block A) with poly(ethyleneglycol) (PEG, block B) prepared by oxidative co-polymerization of aniline with PEG segments that had previously been reacted with p-aminobenzenesulfonyl chloride. The products were reported to be soluble in DMF, DMSO, and THF in the neutral state, but only slightly soluble in the protonated (doped) state. Conductivity of cast films ranged from 0.62 to 1.7×10−4 S/cm (S. Li, H. Dong, Y. Cao, Synthetic Metals, 29, (1989) E329-E336).
Zhang and Bi report the synthesis of polyaniline-poly(phenylene-terephthalamide)-polyaniline tri-block copolymers by reacting low molecular weight poly(phenylene-terephthalamide) terminated with two —COCl groups with low molecular weight polyaniline, previously prepared by oxidative polymerization of aniline in HCl solution (G. Zhang, X. Bi, Synthetic Metals, 41-43, (1991) 251-254).
Kinlen, Frushour, Ding and Menon reported the synthesis of ABA tri-block copolymers where the A blocks are polyaniline and the B block is a α, ω-diamino terminated poly(ethyleneoxide), poly(propyleneoxide), poly(dimethylsiloxane), or poly(acrylonitrile-co-butadiene). Polymerization was performed in emulsion by oxidative coupling of aniline and the α, ω-diamino terminated B block in the presence of dinonylnaphthalenesulfonic acid. Moderately conducting (10−5 S/cm) high molecular weight soluble copolymers were reported (P. Kinlen, B. Frushour, Y. Ding and V. Menon, Synthetic Metals, 101, (1999) 758-761).
Kinlen and others (WO99/16084) report the synthesis of diblock AB and triblock ABA copolymers containing intrinsically conducting blocks (A) and a non-conducting block (B) (FIG. 1, taken from the published application, illustrates the diblock and triblock copolymers). As shown in FIG. 1, diblock copolymers have one non-ICP block and one ICP-block, while triblock copolymers have one non-ICP block and two ICP blocks. The ICP blocks are formed by the polymerization of ICP monomers with the polymerization initiated at a linkage group. The non-ICP blocks have a non-ICP covalently linked with one linkage group (for diblock copolymer) or two linkage groups (for a triblock copolymer) to form a non-ICP precursor. Although the published PCT application mentions the use of ICP monomers including “pyrrole, substituted pyrroles, . . . thiophenes and substituted thiophenes, indoles, . . . furans, carbazoles and mixture thereof . . . substituted and unsubstituted anilines . . . ” the only ICP monomer for which copolymer synthesis is reported is aniline and the only block copolymers exemplified are AB di-block and ABA tri-block copolymers of polyaniline (where the polyaniline block is A). No methods of preparation are provided in the reference for block copolymers containing blocks of poly(heteroaromatic) polymers such as polypyrrole, polythiophene and their derivatives.
There is a significant and continuing need in the art for conducting polymers that exhibit improved processability and mechanical and physical properties. There is a specific need in the art for processable conducting polymers formed from symmetric ICP monomers, such as those containing heteroaromatic monomers.